1. Field
One or more embodiments of the present invention relate to a secondary battery, and more particularly, to a secondary battery including an electrode assembly having an excellent jelly roll structure.
2. Description of the Related Art
Secondary batteries are rechargeable batteries widely used in portable electronic devices such as cellular phones, notebook computers, and camcorders.
A secondary battery typically has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separator wound in a jelly roll shape is enclosed in a case, and the case is covered with a cap assembly. The separator of the electrode assembly is typically formed of an insulating material such as polypropylene (PP) or polyethylene (PE) and is interposed between the positive electrode and the negative electrode to prevent a short circuit between the positive electrode and the negative electrode. Thus, in normal operating conditions, the electrodes are not short-circuited in the electrode assembly of the secondary battery.
However, if a secondary battery is exposed to a high temperature environment, a short circuit may occur. That is, if a secondary battery is exposed to a high temperature environment, the separator insulating the positive electrode and the negative electrode thermally may shrink. Accordingly, the positive electrode may directly contact the negative electrode, and thus a short circuit may occur. The short circuit further may increase the internal temperature of the secondary battery until the secondary battery explodes. In a combustion test in which a secondary battery is heated to 110° C. by using a torch, a separator shrinks and ignition had occurred. Such thermal shrinking starts at the outermost end of the jelly roll structure, which is where external heat first reaches.
Therefore, there is a need to develop a secondary battery that may be safely exposed to a high temperature environment.